- University of Sulaimani

1
1.
2.
3.
Add extra details and polish your scene
Blend colors to achieve such effects as making objects appear
translucent
Smooth jagged edges of lines and polygons with antialiasing
Blending: tells you how to specify a blending function that combines
color values from a source and a destination. The final effect is that
parts of your scene appear translucent.
Antialiasing: explains this relatively subtle technique that alters
colors so that the edges of points, lines, and polygons appear
smooth rather than angular and jagged.
2


With blending, the foreground color is combined with the background
color (translucent)
Without blending, each foreground color overwrites the existing
background color (opaque)
- Linear soft-fill algorithm
3

In the drawing algorithms, all rasterized locations do not match with the
true line, an optimal location is selected to represent a straight line. This
problem is severe in low resolution screens. In such screens line appears
like a stair-step. The effect is known as aliasing.

This effect can be reduced by adjusting intensities of the pixels along the
line. The process of adjusting intensities of the pixels along the line to
minimize the effect of aliasing is called antialiasing.
4







most things in the real world are continuous
everything in a computer is discrete
the process of mapping a continuous function to a
discrete one is called sampling
the process of mapping a discrete function to a
continuous one is called reconstruction
the process of mapping a continuous variable to a
discrete one is called discretization
rendering an image requires sampling and
discretization
displaying an image involves reconstruction
5
6
7
Increasing Resolution
Increase resolution of the raster display. Improvement comes at the
price of memory, bandwidth of memory and scan – conversion time.
1.
8
2. Unweighted Area Sampling
For sloped lines, many times the line passes between two pixels. Line
drawing algorithms select the pixel which is closer to the true line. This
leads to perform antialiasing. In antialiasing instead of picking closest
pixel, both pixels are highlighted. However, their intensity values may
differ.
9
10
3. Weighted Area Sampling
In weighted area sampling equal areas contribute unequally i.e. a small
area closer to the pixel center has greater intensity than does one at a
greater distance. Thus, in weighted area sampling the intensity of the
pixel is dependent on the line area occupied and the distance of area
from the pixel’s center.
11
Point Smoothing
Line Smoothing
glEnable
(GL_POINT_SMOOTH);
glEnable (GL_LINE_SMOOTH);
(no need for blending)
glEnable (GL_BLEND);
glBlendFunc (GL_SRC_ALPHA,
GL_ONE_MINUS_SRC_ALPH
A);
12
13
Review Questions




Explain any two Antialiasing Techniques
How color blending works?
What is aliasing and antialiasing?
Propose some techniques to antialiasing point,
line and polygon.
14